Concrete is the most widely used engineering material in the world. It is estimated that the present world consumption of concrete is 11 billion metric tons per year. (Concrete, Microstructure, Properties and Materials (2006, McGraw-Hill)). Concrete is a term that refers to a composite material of a binding medium having particles or fragments of aggregate embedded therein. In most construction concretes currently employed, the binding medium is formed from a mixture of a hydraulic cement and water.
Hydraulic cements are compositions that set and harden after combining with water. After hardening, hydraulic cements retain strength and stability even under water. The key requirement for this characteristic is that the hydrates that are formed from the hydration of the constituents of the cement are essentially insoluble in water. Cements may be employed by themselves or in combination with aggregates, both coarse and fine, in which case the compositions may be referred to as concretes or mortars, respectively. Most hydraulic cements employed today are based upon Portland cement. Portland cement is made primarily from limestone, certain clay minerals, and gypsum in a high temperature process that drives off carbon dioxide (CO2) and chemically combines the primary ingredients into new compounds.
Carbon dioxide emissions from Portland cement production and other industrial processes such as fossil fuel-based power generation (e.g., coal-fired power plant) contribute to the phenomenon of global warming. It is expected that elevated atmospheric concentration of carbon dioxide and other greenhouse gases will facilitate greater storage of heat within the atmosphere leading to enhanced surface temperatures and rapid climate change. In addition, elevated levels of carbon dioxide in the atmosphere are expected to further acidify the world's oceans due to the dissolution of carbon dioxide and formation of carbonic acid. The impact of climate change and ocean acidification will likely be economically expensive and environmentally hazardous if not timely handled. Sequestration and avoidance of carbon dioxide from various anthropogenic processes offer the potential to reduce risk of climate change.
The invention disclosed herein provides for sequestration and avoidance of carbon dioxide through methods and systems for producing carbonate-containing compositions from material comprising metal silicates, which compositions may be used in concrete.